Photolithography fabrication methods have use in a wide variety of technological applications, including micro-scale and nano-scale fabrication of solar cells, LEDs, integrated circuits, MEMs devices, architectural glass, information displays, and more.
Roll-to-roll and roll-to-plate lithography methods typically use cylindrically shaped masks (e.g. molds, stamps, photomasks, etc.) to transfer desired patterns onto rigid or flexible substrates. A desired pattern can be transferred onto a substrate using, for example, imprinting methods (e.g. nanoimprint lithography), the selective transfer of materials (e.g. micro- or nano-contact printing, decal transfer lithography, etc.), or exposure methods (e.g. optical contact lithography, near field lithography, etc.). Some advanced types of such cylindrical masks use soft polymers as patterned layers laminated on a cylinder's outer surface. Unfortunately, lamination of a layer on a cylindrical surface creates a seam line where the edges of the lamination layer meet. This can create an undesirable image feature at the seam when the pattern is repeatably transferred to a substrate by using the cylindrical mask.
In addition to fabricating a mask having a seamless polymer layer, it would be desirable to fabricate polymer layers with smooth surfaces that are thick and uniform for use in subsequent rolling lithography fabrication methods.
Patterned substrates and structured coatings have attractive properties for a variety of applications, including architectural glass, information displays, solar panels, and more. For example, nanostructured coatings can provide desirable antireflection characteristics for architectural glass. Current methods of patterning substrates, including methods such as electron beam lithography, photolithography, interference lithography, and other methods, are often too costly for practical use in the manufacture of patterned substrates or structured coatings in applications requiring larger areas, especially those having areas of 200 cm2 or more.
As such, there is a need in the art for large area patterned layers and low cost methods of manufacturing the same. It is within this context that a need for the present invention arises.
Nanostructuring is necessary for many present applications and industries and for new technologies and future advanced products. Improvements in efficiency can be achieved for current applications in areas such as solar cells and LEDs, and in next generation data storage devices, for example and not by way of limitation.
Nanostructured substrates may be fabricated using techniques such as e-beam direct writing, Deep UV lithography, nanosphere lithography, nanoimprint lithography, near-field phase shift lithography, and plasmonic lithography, for example.
Earlier authors have suggested a method of nanopatterning large areas of rigid and flexible substrate materials based on near-field optical lithography described in International Patent Application Publication No. WO2009094009 and U.S. Pat. No. 8,182,982, which are both incorporated herein in their entirety. According to such methods, a rotatable mask is used to image a radiation-sensitive material. Typically the rotatable mask comprises a cylinder or cone with a mask pattern formed on its surface. The mask rolls with respect to the radiation sensitive material (e.g., photoresist) as radiation passes through the mask pattern to the radiation sensitive material. For this reason, the technique is sometimes referred to as “rolling mask” lithography. This nanopatterning technique may make use of Near-Field photolithography, where the mask used to pattern the substrate is in contact with the substrate. Near-Field photolithography implementations of this method may make use of an elastomeric phase-shifting mask, or may employ surface plasmon technology, where the rotating mask surface includes metal nano holes or nanoparticles. In one implementation such a mask may be a near-field phase-shift mask. Near-field phase shift lithography involves exposure of a radiation-sensitive material layer to ultraviolet (UV) light that passes through an elastomeric phase mask while the mask is in conformal contact with a radiation-sensitive material. Bringing an elastomeric phase mask into contact with a thin layer of radiation-sensitive material causes the radiation-sensitive material to “wet” the surface of the contact surface of the mask. Passing UV light through the mask while it is in contact with the radiation-sensitive material exposes the radiation-sensitive material to the distribution of light intensity that develops at the surface of the mask.
In some implementations, a phase mask may be formed with a depth of relief that is designed to modulate the phase of the transmitted light by π radians. As a result of the phase modulation, a local null in the intensity appears at step edges in the relief pattern formed on the mask. When a positive radiation-sensitive material is used, exposure through such a mask, followed by development, yields a line of radiation-sensitive material with a width equal to the characteristic width of the null in intensity. For 365 nm (Near UV) light in combination with a conventional radiation-sensitive material, the width of the null in intensity is approximately 100 nm. A polydimethylsiloxane (PDMS) mask can be used to form a conformal, atomic scale contact with a layer of radiation-sensitive material. This contact is established spontaneously upon contact, without applied pressure. Generalized adhesion forces guide this process and provide a simple and convenient method of aligning the mask in angle and position in the direction normal to the radiation-sensitive material surface, to establish perfect contact. There is no physical gap with respect to the radiation-sensitive material. PDMS is transparent to UV light with wavelengths greater than 300 nm. Passing light from a mercury lamp (where the main spectral lines are at 355-365 nm) through the PDMS while it is in conformal contact with a layer of radiation-sensitive material exposes the radiation-sensitive material to the intensity distribution that forms at the mask.
Another implementation of the rotating mask may include surface plasmon technology in which a metal layer or film is laminated or deposited onto the outer surface of the rotatable mask. The metal layer or film has a specific series of through nanoholes. In another embodiment of surface plasmon technology, a layer of metal nanoparticles is deposited on the transparent rotatable mask's outer surface, to achieve the surface plasmons by enhanced nanopatterning.
The abovementioned applications may each utilize a rotatable mask. The rotatable masks may be manufactured with the aid of a master mold (fabricated using one of known nanolithography techniques, like e-beam, Deep UV, Interference and Nanoimprint lithographies). The rotatable masks may be made by molding a polymer material, curing the polymer to form a replica film, and finally laminating the replica film onto the surface of a cylinder. Unfortunately, this method unavoidably would create some “macro” stitching lines between pieces of polymer film (even if the master is very big and only one piece of polymer film is required to cover entire cylinder's surface one stitching line is still unavoidable). It is within this context that the present invention arises.